what's this part of code in exec.start means?
go
Solution
Very Nice find, I did not know that idiom before. I will try to break it down. First We have exec.Cmd
type exec.Cmd struct { ... }
`*Cmd` has 3 many methods including `stdin` `stdout` `stderr`
func (c *Cmd) stdin() (f *os.File, err error) {...}
func (c *Cmd) stdout() (f *os.File, err error) {...}
func (c *Cmd) stderr() (f *os.File, err error) {...}
Now I want to call all these functions and do the same set of operations on each of them but I don't want to create another method because there are too many shared variable to pass by arguments.
The first solution would be to just copy / paste the code 3 times. not nice.
The second is to loop over an array of Functors. The Functor type would be `func(c*Cmd)(f *os.File, err error)` so we declare it as
type F (c *Cmd) (f *os.File, err error)
now we can create the array of functors. But how to select a `*Cmd` method ? simply using
`(*Cmd).<name of method>`
So it would be `(*Cmd).stdin, (*Cmd.stdout), (*Cmd).stderr` and we can use them as An array
[]F{ (*Cmd).stdin, (*Cmd.stdout), (*Cmd).stderr }
we just need to call them now
for _, setupFd := range []F{(*Cmd).stdin, (*Cmd).stdout, (*Cmd).stderr} {
fd, err := setupFd(c)
...
}
Hope this helps.
Problem
I read the code of exec.Start,and there some part confusing me. (*Cmd).stdin/out/err in the []F,what's the meaning of (*Cmd).stdXX? ``` 291 type F func(*Cmd) (*os.File, error) 292 for _, setupFd := range []F{(*Cmd).stdin, (*Cmd).stdout, (*Cmd).stderr} { 293 fd, err := setupFd(c) 294 if err != nil { 295 c.closeDescriptors(c.closeAfterStart) 296 c.closeDescriptors(c.closeAfterWait) 297 return err 298 } 299 c.childFiles = append(c.childFiles, fd) 300 } ```